1. Technical Field of the Invention
The present invention relates to an illumination device and a projection display device using the same, and more particularly, is suitable for use with a laser light source as an emission light source.
2. Disclosure of the Related Art
Conventionally, in a projection display device (hereinafter, referred to as a “projector”), there has been used a lamp light source such as an ultra-high pressure mercury lamp, a metal halide lamp, or a xenon lamp, as an emission light source. Also, in recent years, a projector incorporated with a solid-state light source such as a semiconductor laser, as an emission light source, has been developed. The laser light source has been noticed as an emission light source for a next-generation projector, in view of a point that the laser light source has a superior performance of rendering a wide color space with high luminance and high precision. In addition, an optical system using a fly-eye lens is widely used as an illumination device of a projector.
In the case where a laser light source operable to emit a light flux having a large solid angle is used as an emission light source, it is necessary to properly convert laser light emitted from the laser light source into parallel light and enter the light into a fly-eye lens. In converting laser light into parallel light by using a lens, a diffraction grating, or the like, an intensity distribution of laser light to be obtained after transmission through the lens, the diffraction grating, or the like may become non-uniform.
FIG. 14B is a diagram schematically showing in monochromatic expression an intensity distribution of a flux of laser light emitted from a laser light source which is converged and converted into parallel light by a cylindrical lens in an Y-axis direction as shown in FIG. 14A, the intensity distribution being determined by the use of an optical simulation software program. In the diagram, the light intensity is higher with increasing proximity to white. In this arrangement, the light intensity distribution is non-uniform in the Y-axis direction.
This phenomenon also takes place when a plurality of laser light sources are arranged in an array. FIG. 14D is a diagram schematically showing in monochromatic expression a light intensity distribution obtained by arranging five laser light sources in an X-axis direction, converging and converting laser light from the laser light sources into parallel light equally in the Y-axis direction by a horizontally long cylindrical lens as shown in FIG. 14C, the light intensity distribution being determined by the use of an optical simulation software program. As in the case with FIG. 14B, the light intensity is higher with increasing proximity to white. Here, light intensity is approximately uniform in the X-axis direction but is non-uniform in the Y-axis direction.
If a normal fly-eye lens is used to superimpose light of non-uniform intensity as above, the number of patterns of light superimposition is decreased. Accordingly, illuminance non-uniformity occurs on an imager (such as a liquid crystal panel), which leads to unevenness of an image projected onto a screen.
Illuminance non-uniformity can be suppressed by narrowing a cell pitch of the fly-eye lens to increase the number of light superimpositions. However, decreasing a cell pitch may raise the rate at which light is attenuated due to a shear droop between cells at the time of lens formation, resulting in reduced light use efficiency. In addition, with a narrow cell pitch, illuminance non-uniformity may occur in illumination light due to other factors such as interference fringes.